1. Field of the Invention
The present invention relates to a wiring electrode for semiconductors and a manufacturing method thereof. Particularly, the present invention relates to a metal system of an electrode which has an aluminum alloy wiring layer (hereinafter, referred as an Al alloy layer) and can reduce the defects (called Al void) that occur within Al alloy layers due to the miniaturization.
2. Related Arts
In recent years, with the advancements in technology for integrating elements, technologies for miniaturization and multilayering have become essential. As miniaturization advances, the need to design finer widths for the wiring in the Al alloy layer arises. But, as shown in FIG. 4, as the wire widths become finer than 2 .mu.m or 3 .mu.m, especially less than 1 .mu.m, Al voids are known to occur inside the Al alloy layer. Such Al voids are generated as a stress migration due to the tensile stress which occurs inside the Al alloy layer during heat treatment. Also, the Al voids occur when various thin films are multilayered because such multilayered structure causes tensile stress inside the element.
If these Al voids become significantly large, the reliability factor becomes a big problem. For example, the following problems may occur: disconnection of the Al alloy wiring; increase in the wiring resistance due to the reduction in the cross section of the Al alloy layer; destruction of the elements due to heat generation; delays in the operation speed; electromigration due to the application of large current and the like.
One conventional method, that has been used to reduce the occurrences of Al void is to mix copper in the aluminum and silicon (Al--Si) wiring electrode to form the Al--Si--Cu wiring, wherein the copper acts to hinder the movement of the Al atoms.
Such wiring electrode is disclosed in JP-A-63-152147. The publication discloses that, if the crystal surface of the Al--S--Cu wiring is oriented at the (111) plane, the occurrence of Al voids is further reduced. In other words, as the (111) plane is filled most densely with Al atoms, the movement of an Al atom is restrained by the other Al atoms, or movement of the Al atoms for easing the tensile stress inside the Al alloy layer is restrained, which leads to fewer occurrences of Al voids.
However, the (111) plane orientation of the Al--Si--Cu wiring has a close relation to the underlying crystal structure. For example, as disclosed in JP-B-3-3395, JP-A-4-42537 and JP-A-3-262127, it has been discovered that it is difficult to properly orient the crystal surface of the Al alloy when a metallic nitride film of high melting point, like a titanium nitride (TiN) layer, is interposed under the Al alloy layer as a barrier metal.
Thus, for the wiring electrode disclosed in JP-A-63-152147, the underlying crystal structure needs to be supervised carefully to improve the orientation of the Al--Si--Cu wiring, and because of this, improvements in the productivity cannot be expected.